Here's a picture of my latest creation. This will go into a 1981 Chevy PU with a built 350 engine. This trans has a lock-up torque converter, deep pan, red line frictions, Kolene steels, and a Gil Younger shift kit - it will be ausome.
This is the kick down cable where it attaches. One bolt holds it on. Later trans used a 10mm socket, but one as early as yours probably uses a 3/8 or 7/16.
The cable is hooked to a small rod.
The small rod looks like this - you can see it doesn't take much foolin around to connect it.
There is a small "O" ring that seals the end of the cable housing - don't forget this or it will leak. Let me know if you need the bolt size and thread pitch - I've got a couple dozen laying around here and there.